The present invention relates to a rope gripper which may be used with a rope operated switch assembly. Such an assembly may be used, particularly but not exclusively, for controlling the power supply to kinetic machinery.
Rope operated switch assemblies are generally fitted in proximity to a machine or around any area which requires protection, and generally comprise two safety switches and a rope connected to each of the switches using thimbles and cable clamps such that the electrical power supply may be turned off when the rope is pulled or slackened (e.g. if the rope is cut). In some applications, only one switch is provided, one end of the rope being connected to the single switch and the other end being connected to for example a spring secured to a fixed point. The rope is generally a plastics-coated metal wire or cable, and extends around the machine so that an operator can easily reach it from any position adjacent the machine. The term xe2x80x9cropexe2x80x9d used hereinafter is intended to mean any elongate flexible element that is suitable for use in a rope operated switch assembly, for example, metal cable, cord formed of twisted elements or fibres such as wire, polymeric material, etc., which may optionally be coated with a plastics material.
The rope must be installed at the correct tension so that the machinery can be operated. Thereafter a relatively small change in the tension of the rope must actuate the switch assembly. This is important because an injured operator may not be able to pull the rope with much force.
The installation of the rope at the correct tension is difficult to achieve. The rope must first be installed between the two switches, and is then pulled tight to an approximation of the correct tension. The tension can be adjusted using a turnbuckle installed in the centre of the rope by cutting the rope and fixing the turnbuckle between the rope sections using thimbles and cable clamps. Once installed, the tension in the rope is set by adjusting eye bolts on the turnbuckle until the rope switches are pulled into a xe2x80x9crunxe2x80x9d position, that is, with safety contacts in the switches made. The turnbuckle then allows small alterations to be made to the tension of the rope to allow for expansion or contraction of the rope due to, for example, temperature differences. Thus in most applications four rope ends must be connected either to a rope switch or to a turnbuckle. The making of such connections can take up a large proportion of the total time taken to install the rope switch assembly.
It is an object of the present invention to obviate or mitigate the above disadvantages by providing a rope gripper which can be used to simplify the process of attaching a rope to for example a rope switch.
According to the present invention there is provided a rope gripper comprising a body defining a passage into which a rope to be gripped may be inserted, and at least one jaw displaceably mounted adjacent the passage and biased towards a position in which it engages an inserted rope, the at least one jaw being shaped and mounted such that movement of an inserted rope in one direction relative to the passage drives the jaw towards a position in which the rope is jammed within the passage and movement of the rope in the opposite direction drives the jaw to a position in which the rope can slide past the jaw.
Thus, a rope switch installation can be set up quickly and easily simply by positioning rope switches in appropriate locations, coupling rope grippers to each of those rope switches, and pulling rope ends through the rope grippers until an appropriate rope tension has been achieved. If fine control of the rope tension is required, a tensioning device such as a turnbuckle can be introduced into the rope by connecting rope grippers in accordance with the invention to the turnbuckle, cutting the rope, and then attaching the cut rope ends to the turnbuckle using the rope grippers. With such an arrangement, installers do not have to spend time manipulating conventional cable clamps and associated components.
Preferably the or each jaw is eccentrically mounted on a pivot pin such that rotation of the jaw as a result of rope movement in the rope jamming direction causes the jaw to progressively obstruct the passage, thereby increasing pressure on the rope until further rope movement is prevented. Two jaws may be arranged on opposite sides of the passage, and the jaws may be biased inwards towards the passage by springs depending from an annular spring member extending around the passage.
Preferably the passage comprises a first straight section which extends from a rope receiving aperture at one end of the body to a second straight section which extends to a rope exit aperture on one side of the body, means being provided at the end of the body remote from the receiving aperture for connecting the body to a further device such as a rope switch or a rope tensioning device such as a turnbuckle.
The invention also provides a method for installing a rope switch using a gripper as defined above and coupling that gripper to an actuator of a rope switch.